Paper for roll photographic film



United States Patent PAPER FOR ROLL PHOTOGRAPHIC FILM Ernest L. Baxter, New York, N. Y., assignoitto- Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application April 10, 1953, Serial No. 347,983 7 Claims. (Cl. 117--14 This invention relates to improvements in backing paper for roll photographic film, and more particularly relates to a backing paper with protective light-colored and opaquing coatings thereon, which has appreciably less overall thickness than conventional backing papers,' and which is superior in opaqueness and equal in other respects to presently employed duplex backing paper.

The backing paper of this invention is an improvement over that described and claimed in my copending patent application Ser. No. 187,124, filed September 27,- 1950,

now Patent 2,646,365 and is a continuation-in-part of my copending application Ser. No. 260,714, filed- December 8, 1951, now Patent 2,646,366 of July 21,- 1953.

As is Well understood, a photographic roll film cartridge generally comprises a flanged. spool upon which is wound a long strip of backing paper to which before winding has been attached a strip of light sensitive photographic film. The ends of the backing paper are positioned to extend beyond the ends of the film andcon'sti'- tute light protective leader and trailer strips for thefihn which is interwound with the backing paper and, therefore, separates adjacent convolutions of the film.

In a commonly available roll film cartridge, the film is attached to the black side of a duplex backing paper, the side of the backing paper opposite that contacting the film is dilierently colored and carries various printed symbols such as the number ofthe exposed areas,-warn=- ing marks, and advertising matters, over which is coated a protective layer intended to protect the sensitive emulsion fromv the paper and ink imployed imprinting when the film and paper are interwound inclose contact. It has been the practice to depend somewhat on the" paper itself to prevent the transmission of light; .To assure opaqueness, backing paper presently employed for roll films consists of a duplex paper with o'ne'sidebeing black and the other side colored with a characteristic identifying, color. Thepaper may be made by means of a Fourdrinier paper machine and a cylinder paper machine; The two sheets are brought together wet under the first press and thus form a composite sheet of duplex backing paper.

Duplex backing paper which is thus processed has cer tain definite specifications that must be met. The black side must be opaque and free from pinholes. er colored side should be uniform in color and appear"- ance and should not permit any of the black on the opposite side to be visible through the paper. The diameter ofthe finished spool. of roll film, and, therefore, the number of exposures, is dependent on the overall thickness of the coated backing paper and the film,.s'o thickness of the paper itself must belimited. The requiredstrength. of thepaper which is important both in the camera in processing, also limits the thinness of the papen- Either black numerals on a white paper or whitenumerals'on-ablack paper gives the greatest contrast, but neither. paper is. verypleasing to the eye. Lighter colored haclt'grounds such. as shades of. red, green, yellow and blue: are most desirable from an appearance standpoint,-

Tlie light-.

v quired tohide the black side and to give the light colored side a uniform appearance. The present invention, however, provides a thinner backing paper which does not have a duplex structure but which has superior characteristics in several important respects.

An object, therefore, of the present invention is to pro.- vide a backing paper comprising a single sheet of paper, as contrasted to a duplex paper, which has" a strength at least equal to the thinnest duplex papers now prednced..

Another object of the invention is to provide asingle sheet coated backing paper which is not only thinner than present duplex paper, but has an opaqueness superior to such duplex backing papers.

Another object of the invention is to provide a thin single sheet backing paper, the opacity of which is dependent primarily on the chemical coatings on the paper rat-her than the paper structure itself.

Still another object is to provide a backing paper having an improvement in overall thinness so that extra film exposures are permitted without increasing the diameter of the roll beyond that of the same type of presently employed roll film.

Yet another object is to provide a backing. paper comprising a single sheet of paper with black opaquing coatings thereon which are more flexible than those black coatings on the backing papers described in my copending applications Ser. No. 187,124, filed September 27, 1950, new Patent 2,646,365 and Ser. No. 260,714, filed December 8', 1951, now Patent 2,646,366 of July 21', 1953.

In accordance with the present invention these and other objects are attained by employing as the paper strip in thebacking paper a single sheet, as contrasted to a duplex paper, which has been supercalendered to a thickness appreciably less than commonly employed duplex papers. By itself this paper is so thin that it transmits sufiicient actinic light to cause film exposure. This singlepaper is then coated on one side with a black opaque coating and on the other side by a composite coating of lighter colored composition. The paper may then be printed on the lighter colored side and, if so printed, the printed side is given a transparent protective overcoating to protect the film emulsion from the printing inks'. The various coatings may be applied in proper sequen'ce' by a rotogravure process or by other suitable coating processes such as described hereinafter. The coatings may be suitably dried between applications.

The paper preferably employed as the base of the ba'cking; paper structure is a IS-pound per 1000 sq. ft.- p'aper made of a purified fiber or of unpurified fiber such as unbleached natural color kraft paper which is conditioned to 442% moisture content andsupercalendered td' a thickness of 0.0025 to 0.0030 inclL- This thin single sheet paperis then coated on one side with a black coating'. The opposite side of this thin paper is coated with a yellow coating. The compositions of the black and yellow coatings are described hereinafter. The thus coated-paper is printed on the yellow side with suitable legends and overcoated with a transparent rotective coating to protect the film emulsion from the printing inks when the film and backing paper is rolled onto the film spool.

One ofthe following three black coating compositions may be advantageously employed for preparing'a backing paper in accordance with my present invention:

- 3 BLACK commas The following three examples describe the composition of suitable black opaquing coatings.

Example I Y Percent Vinylidene chloride-acrylonitrile copolymer (51.5 to

53% of solids) 28.0 Paris black (carbon) 13.4 Water 57.8

Sodium salt of partially desulfonated lignin sulfonic acid 0.7 Triton X-100 (an alkylated aryl polyether alcoho containing 20% butyl phthalate) 0.5

Example II Percent Styrene-butadiene copolymer (50-70% styrene) (48% solids in aqueous colloidal dispersion) 21.6

Carbon black 14.8 Sodium salt of partially desulfonated lignin sulfonic acid 0.75 NaOH 0.014 Water 62.8

Example III Percent Styrene-butadiene copolymer (50-70% styrene) (48% solids in aqueous colloidal dispersion)--- 19.8

Carbon black 16.0 Water 63.3 Sodiumsalt of partially desulfonated lignin sulfonic acid 0.80 NaOH 0.08

In preparing the black colored dispersions the selected resin copolymers is added with stirring to a 30-40% aqueous carbon dispersion. The carbon dispersion is made by adding the carbon to water containing as a dispersing agent the sodium salt of the partially desulfonated lignin sulfonic'acid and caustic soda is added to control the pH within the range of 10:1.

The black coating of Example III is preferred.

YELLOW COATINGS The following three compositions may be employed for coating the light colored side of the backing paper.

Example IV Pounds Zein 20 Medium chrome yellow 10 Light orange (chrome) Q. 5 Titanium dioxide 15 Isopropyl alcohol 64 Water 16 Example V Percent Styrene-butadiene copolymer (50 to 70% styrene) The yellow coating of Example V gives a very uniform flexible light colored side which is superior to the coating of Example IV which is somewhat more brittle and eventually has a poorer color because of the darkening of the yellow pigment by the zein.

In these formulas the titanium dioxide pigment is finely divided; medium chrome yellow is a finely divided metal chromate pigment; light orange is a finely divided metal chromate pigment. Zein is employed as the binder in the yellow coating of Example IV and the protective overcoating since it will not fog or desensitize the photographic emulsion of the film.

A suitable rotogravure process for applying these coatings to the paper base of the backing paper is described in U. S. Patent 2,218,249 of October 15, 1940. The various applications are made continuously and each coating is dried before the next is applied. The coating is applied to the paper by the intaglio roll which rotatably mounted in a pan containing the coating solution. The surface of the intaglio roll is embossed providing a plurality of very minute cups which carry the solution, the excess solution being removed from the intaglio roll by a doctor blade. The solution in these various cups is then transferred or applied uniformly to the strip by pressing the strip firmly against the cups by means of a rubber pressure roll over which the strip is fed. Each of these deposits after being placed on the paper is merged into a continuous layer by means of a smoothing bar to provide a uniform coating over the entire paper surface. Each coating is preferably dried in heated air having a relative humidity of 6% at 170' F. before applying a second coating.

The various coatings described herein may also be applied to my backing paper base by the roll and air knife method generally described in Patent 1,980,923 of November 13, 1934. The selected black coating is applied first to one side of the single sheet backing paper and spread -by the air knife. This black coating is dried at l-200 F. by being passed through a heated drying chamber. In some instances a plurality of black coatings may be spread onto the black side of the backing paper by alternate coating and drying steps. If desired a final wash of 20% zein is applied to prevent blocking before the paper is rolled up.

Suitable ink compositions for printing indicia by rotogravure processes on the backing paper are disclosed in my Patent Re. 21,268 of November 21.v 1939. These inks comprise suitable coloring materials in a prolaminc binder such as zein. Other suitable printing inks for such backing papers are disclosed in my Patent 2,262,986 of November 18, 1941.

The invention will be further understood by reference to the drawings in which Figs. 1 to 6 represent a greatly enlarged cross-section of backing paper made in accordance with various forms of my present invention. and Fig. 7 shows the novel backing paper of Fig. 3.and photographic film wound on the roll with the film and backing paper separated at one end for purpose of illustrating their relative positions in the roll.

Referring to Fig. l, a cross-section of a strip of unbleached kraft paper is shown at 10 having thereon a coating 11 of a layer of carbon black in a vinylidene chloride-acrylonitrile copolymer coated from the composi tion of Example I. On the opposite side of the paper 10; there isthe yellow coating 13 comprising chrome orange and yellow pigments as well as titanium dioxide pigments in a zein binder. This was coated from the composition found in Example IV, supra. The printed indicia is shown at 16 overcoated with a transparent protective zein coating 15. Such a transparent zein protective coating is described in my Patent 2,262,987 of November 18, 1941.

Referring to Fig. 2 a cross-section of a strip of unbleached kraft paper is shown at 20 having thereon a coating 21 of a layer of carbon black in a styrenebutadiene copolymer coated from the composition 'of Example III. On the opposite side of the paper 20 there is a yellow coating 23 comprising chrome yellow and titanium dioxide in a zein binder which is coated from the composition of Example IV. This was coated onto the backing paper base from the composition of Example IV. The printed indicia is shown at 26 overcoated with a transparent protective zein coating 25. This coating is similar to the coating 15 of Fig. 1.

Referring to Fig. 3 a cross-section of a strip of unbleached kraft paper is shown at 30 having thereon a coating 31 of a layer of carbon black in a vinylidene chlorideacrylonitrile copolymer coated from the composition of Example I. On the opposite side of the paper 30 there is a yellow coating 33 comprising chrome yellow and titanium dioxide in a styrene-butadiene copolymer. This was coated onto the backing paper base from the composition of Example V. The printed indicia is shown at 36 overcoated with a transparent protective zein coating 35. This zein coating is similar to the coating 15 of Fig. 1.

Referring to Fig. 4 a cross-section of a strip of unbleached kraft paper is shown at 40 having thereon a coating 41 of a layer of carbon black in a styrene-butadiene copolymer coated from the composition. of Example II. On the opposite side of paper 40 there is a yellow coating 43 comprising chrome yellow and titanium dioxide in a styrene butadiene copolymer. This was coated onto the backing paper from the composition of Example V. The printed indicia is shown. at 46 overcoated with a transparent zein coating 45 which is of a composition similar to that coating 15 of Fig. 1.

Referring to Fig. a cross-section of a strip of unbleached kraft paper is shown at 50 having thereon a coating 51 of a layer of carbon black in vinylidene chloride-acrylonitrile copolymer from the composition of Example I. On the opposite side of paper 50 there is a yellow coating 53 comprising chrome yellow and titanium dioxide in a vinylidene chloride-acrylonitrile copolymer coated from the composition of Example VI. This was coated onto the paper from the composition of Example VI. The printing is shown at 56 overcoated with a trans parent zein coating 55 which is a composition. similar to that coating 15 of Fig. 1.

Referring to Fig. 6 a cross-section of a strip of unbleached kraft paper is shown at 60 having thereon a coating 61 of a layer of carbon black in a styrene-butadiene copolymer coated from the composition of Ex.- ample II. On the opposite side of paper 60 there is a yellow coating 63 comprising chrome yellow and titanium dioxide in a vinylidene chloride-acrylonitrile copolymer coated from the composition of Example VI. The printing is shown at 66 overcoated with a transparent zein coating 65 which is a composition similar to that coating 15 of Fig. 1.

The backing paper structure described. in connection with Fig. 3 is the preferred form of the present invention. However the backing paper structures shown in Figs. 1 to 6 give a product that fulfills all the advantages described in my copending applications, supra, at a great reduction in cost and at the same time results in amore flexible product which does not produce harmful dust when wound through a camera.

Referring to Fig. 7', a film cartridge 70 is shown partly open in which the backing paper of the present invention is employed. This figure shows the relation of the backi'ng paper surfaces 31 and'35 of Fig. 3 in respect tothe film 73 when assembled on the spool. The emulsion side of the film is shown at 71 and the base side at 72.

Although I prefer for the yellow coating a butadienestyrene copolymer having, approximately 60% styrene, other similar proportions may be used. However as the styrene content of the resin falls below 50% the com position becomes. somewhat tacky. As the styrene content. rises. above 70% the composition. becomes somewhat brittle. The vinylidene chloride-acrylonitrile copolymer 6 may advantageously contain 15% acrylonitrile and 85% vinylidene chloride. I

I have found that by employing an initial coating of carbon black in the above resinous matrices on the black side of the paper, the resulting backing paper structure has considerable improvement in respect to flexibility of the black side without loss of resistance to scratching and abrasion. In this respect the backing paper of the present invention is superior to that described and claimed in. my copending applications Ser. Nos. 187,124 and 260,714 supra. These resinous binder coatings are less brittle than a zein-black or vinylacetate-black coating of a corresponding thickness.

While the preferred coating compositions are described above, satisfactory backing papem may be made by employing the various coating materials in the following ranges:

Compositions Preferred Range vinylidene chloride-acrylonltrile copolymer or 5 to 25%.

Styrene-butadiene copolymer.

Black pigmpnt 1 to 20% White pigment 15 to Yellow ni me 15 to 45%.

Water to of total composition.

Other useful pigments are, for example, Hansa Yellow, Fast Pigment Yellow and any carbon black of suitable dispersion.

Other pigments which are inert to photographic emulsions may be employed. In fact, any choice of pigments of suitable size for this invention is limited only by the requirement that they be without detrimental effect on the photographic film.

THICKNESS oF COATING Black coating composition is applied in two coatings to give a total of 12 lbs. of solution per 1000 sq. foot for satisfactory opacity.

Light pigment composition is applied in the amount of 4% lbs. per 1000 sq. foot to give satisfactory uniformity of color.

Any other type of paper; may be employed if it has good strength at least comparable to the present duplex paper. A rag paper, for example, is suitable but, of course, more expensive than kraft paper.

COMPARISON OF DURLEX AND TEA-R Preferably the average tear strength of a suitable paper should be at least 50' grns; as determined by the Elm'endorf tear test. This tear test is described in- Paper Trade Journal for June' I8, 1942, as Tappi Standard T 414 M 40.

While, as indicated above, tan krafitv paper is' particularly suited for employment in my invention, certain other types of paper could' be employed instead, such as unbleached. sulfate paper colored with a suitable dye such as Stilbene yellow in which a small amount: of filler such as TiOz is added togive body and density or opacity to the paper.

These papers comprising the base of the backing paper are of a weight that can: be. supercalcndered to 'a ness that the paper itself plus the coatings thereon docs not exceed a thickness of 0.0040 inch. A

pound per M sq. ft. paper has been found satisfactory.

The opacity of roll film backing paper is tested in the following manner.

A sheet of the backing paper under test is placed over a sheet of highly sensitive film, such as Super XX Pan- -chromatic film with the black side of the backing paper in contact with the back of the film, duplicating its position on roll film. An orange-red filter of the type employed in camera back windows is placed over the opposite side of the backing paper and the assembly is placed in a printing frame. The test material is exposed to a light intensity of 5000 foot candles for ten minutes. The film is then processed in the usual way and examined for the presence of specks of developed silver. A satisfactory "backing paper should show no visible silver image.

The improvement in employing the resinous coatings of the present invention as respects flexibility is shown in the following table:

, (The higher the number the stifier the paper.)

I 'Ia'ppi Tentative Method T461. 1 Tappi Instrumentation Studies XIV.

I have found that my improved backing paper has many advantageous features not possessed by duplex papers which it may replace. The strength and other physical properties of the paper employed as the base of the backing paper is at least equal to the strength of the thinner duplex papers now available to the trade. The overall thickness can be made as low as 0.0032 up to 0.0040 inch thus permitting extra exposures to be added to present rolls of film without increasing the diameter beyond that of films now in use. The 'opaqueness, even though the overall thickness is less than backing papers now available in the trade, is better than such backing papers. The backing paper made in accordance with my invention requires the least amount of coating materials, both black and colored, of any of the methods described or known in the trade. The uniformly light colored side gives maximum contrast with the legends printed thereon. Also less clock springing of freshly rolled film is experienced-with this paper than with the thicker duplex paper. These advantages plus the advantage of applying the coatings by rotogravure and air knife methods, which are fast, accurate and efficient, emphasize the importance of my present invention iri this art.

I claim:

l. Photographic backing paper having an overall thickness less than 0.0040 inch comprising a single sheet of kraft paper, as contrasted to a sheet of duplex paper, of a thickness of approximately 0.0026 inch which will permit passage of substantial amounts of actinic light, having on one side an opaquing coatingv composition comprising carbon black in a binder selected'from the class consisting of vinylidene chloride-acrylonitrilecopolymer and styrene butadiene copolymer, alighter colored pig mented coating on the opposite surface of the paper comprising a yellow pigment in a binder selected from the class consisting of vinylidene chloride-acrylonitrile copolymer, styrene-butadienecopolymer and zein, printing on said colored coating, and a clear zein protection 'coatingthereover, the complete backing paper structure being sufliciently opaque to prevent actinic light from passing therethrough.

2. Photographic backing paper having an overall thickness less than 0.0040 inch comprising a single sheet of kraft paper, as contrasted to asheet of duplex paper, of a thickness of approximately 0.0026 inch which will permit passage of substantial amounts of actinic light, having on one side an opaquing coating composition comprising carbon black in a vinylidene chloride-acrylonitrile copolymer binder, a lighter colored pigmented coating on the opposite surface of the paper comprising a yellow pigment in a zein binder, printing on said colored coating, and a clear zein protection coating thereover, the complete backing paper structure being sufiiciently opaque to prevent actinic light from passing therethrough.

3. Photographic backing paper having an overall thickness less than 0.0040 inch comprising a single sheet of kraft paper, as contrasted to a sheet of duplex paper, of a thickness of approximately 0.0026 inch which will permit passage of substantial amounts of actinic light, having on-one side an opaquing coating composition comprising carbon black in a styrene-butadiene copolymer binder, a lighter colored pigmented coating on the opposite surface of the paper comprising a yellow pigment in a zein binder, printing on said colored coating, and a clear zein protection coating thereover, the complete backing paper structure being sutiiciently opaque to prevent actinic light from passing therethrough.

4. Photographic backing paper having an overall thickness less than 0.0040 inch comprising a single sheet of kraft paper, as contrasted to a sheet of duplex paper, of a thickness of approximately 0.0026 inch which will permit passage of substantial amounts of actinic light, having on one side an opaquing coating composition comprising carbon black in a vinylidene chloride-acrylonitrile copolymer binder, a lighter colored pigmented.

coating on the opposite surface of the paper comprising a yellow pigment in a styrene-butadiene binder, printing on said colored coating, and a clear zein protection coating thereover, the complete backing paper structure being sufficiently opaque to prevent actinic light from passing therethrough.

5. Photographic backing paper having an overall thickness less than 0.0040 inch comprising a single sheet of kraft paper, as contrasted to a sheet of duplex paper, of

a thickness of approximately 0.0026 inch which will permit passage of substantial amounts of actinic light, having on one side an opaquing coating composition comprising carbon black in a styrene-butadiene copolymer binder, a lighter colored pigmented coating on the opposite surface of the paper comprising a yellow pigment in a styrene -butadiene binder, printing on said colored coating, and a clear zein protection coating thereover,

the complete backing paper structure being sulficientlyopaque to prevent actinic light from passing therethrough.

6. Photographic backing paper having an overall thickness less than 0.0040 inch comprising a single sheet of kraft paper,'as contrasted to a sheet of duplex paper, of a thickness of approximately 0.0026 inch which will permit passage of substantial amounts of actinic light, having on one side an opaquing coating composition comprising carbon black in a vinylidene chloride-acrylonitrile copolymer binder, a lighter colored pigmented coating on the opposite surface of the paper comprising yellow pigment in a vinylidene chloride-acrylonitrile copolymer,.

9 site surface of the paper comprising yellow pigment in a vinylidene chloride-acrylonitrile binder, printing on said colored coating, and a clear zein protection coating thereover, the complete backing paper structure being sufiiciently opaque to prevent actinic light from passing 5 therethrough.

UNITED STATES PATENTS Baxter May 16, 1939 Baxter Nov. 18, 1941 Baxter July 21, 1953 Baxter July 21, 1953 

1. PHOTOGRAPHIC BACKING PAPER HAVING AN OVERALL THICKNESS LESS THAN 0.0040 INCH COMPRISING A SINGLE SHEET OF KRAFT PAPER, AS CONTRASTED TO A SHEET OF DUPLEX PAPER, OF A THICKNESS OF APPROXIMATELY 0.0026 INCH WHICH WILL PERMIT PASSAGE OF SUBSTANTIAL AMOUNTS OF ACTINIC LIGHT, HAVING ON ONE SIDE AN OPAQUING COATING COMPOSITION COMPRISING CARBON BLACK IN A BINDER SELECTED FROM THE CLASS CONSISTING OF VINYLIDENE CHLORIDE-ACRYLONITRILE COPOLYMER AND STYRENE BUTADIENE COPOLYMER, A LIGHTER COLORED PITMENTED COATING ON THE OPPOSITE SURFACE OF THE PAPER COMPRISING A YELLOW PIGMENT IN A BINDER SELECTED FROM THE CLASS CONSISTING OF VINYLIDENE CHLORIDE-ACYLONITRILE COPOLYMER, STYRENE-BUTADIENE COPOLYMER AND ZEIN, PRINTING ON SAID COLORED COATING, AND A CLEAR ZEIN PROTECTION COATING THEREOVER, THE COMPLETE BACKING PAPER STRUCTURE BEING SUFFICIENTLY OPAQUE TO PREVENT ACTINIC LIGHT FROM PASSING THERETHROUGH. 